Dear Auge

I read the Note:
Note: The Windows implementation of mail() differs in many ways from the Unix implementation. First, it doesn't use a local binary for composing messages but only operates on direct sockets which means a MTA is needed listening on a network socket (which can either on the localhost or a remote machine).
Second, the custom headers like From:, Cc:, Bcc: and Date: are not interpreted by the MTA in the first place, but are parsed by PHP.
As such, the to parameter should not be an address in the form of "Something <someone@example.com>". The mail command may not parse this properly while talking with the MTA.

I think I must be really dumb because I cannot make any head-or-tail of using this info.

My Windows server can send emails through (and these get delivered):
<?php
if(mail('email@my_domain.com','test subject','test message')){
echo('ok');
}
else{
echo('not ok');
}
?>

(for above, the sender is the default email ID of the server)

I guess this means the issue is Not of MTA (at my server).

I have also tried this successfully with multiple recipients:
<?php
if(mail('email_1@my_domain.com,email_2@other_server.com','test subject','test message')){
echo('ok');
}
else{
echo('not ok');
}
?>

(for above, the sender is the default email ID of the server)

I would really appreciate if you can help me (and other Windows server "sufferers") with this issue.

Namaste

Vinayy